Film multilayer body and flexible circuity board

ABSTRACT

A film laminate permitting the formation of a fine pattern and being excellent in electrical reliability is provided. The film laminate is characterized in that a plasma CVD layer of an organic metal compound and an electrically conductive layer are successively formed on at least one side of a heat-resistant polymer film.

TECHNICAL FIELD

The present invention relates to a film laminate and a flexible circuitboard obtainable from the film laminate.

BACKGROUND ART

In recent years, the density of pixels has become higher and higher inflat panel displays such as liquid crystal displays. It is, therefore,necessary that flexible circuit boards connected to the displays havehigh precision patterns. At the same time, it is important to ensureelectrical reliability as the pitch of the patterns is narrowed.

Conventionally, copper clad laminates for flexible circuit boards havebeen produced by bonding a polyimide film to a surface-roughed copperfoil using an adhesive such as an epoxy adhesive.

As problems of such a technique, lack in heat resistance and lack inelectrical reliability have been pointed out.

To cope with these problems, a method is proposed in which a polyimideresin is directly applied on a copper foil by coating. Since the copperlayer of the copper clad laminate is thick, however, it is difficult toensure desired process precision of the fine pattern in the wiring boardobtained by etching the copper of the laminate.

A method for preparing a copper clad laminate having a high adhesionstrength without using an adhesive is also known in which, after a metallayer different from copper, such as nickel or chromium, has been formedas a primer layer on a polyimide film by sputtering or vapor deposition,electrolytic copper plating is performed. This method, however, causes aproblem of delamination during implement because the adhesion strengthis not fully satisfactory. Additionally, since the metal of the primerlayer is apt to remain removed during the etching, the electricalreliability is not high. Further, a problem of a significant reductionof the adhesion strength is caused when a heat treatment is carried outfor a long time.

It is an object of the present invention to provide a film laminatewhich permits the formation of fine patterns with ease and which hasexcellent electrical reliability and to provide a flexible circuit boardobtainable from the laminate.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided a filmlaminate including a heat-resistant polymer film, a plasma CVD layer ofan organic metal compound provided on at least one side of theheat-resistant polymer film, and an electrically conductive layerprovided on the plasma CVD layer.

The present invention also provides a flexible circuit board includingthe above film laminate in which the electrically conductive layer ispatterned to form a circuit, and a copper plating layer provided on thecircuit.

The present invention further provides a flexible circuit boardobtainable by a method including forming a photosensitive resin over theelectrically conductive layer of the above film laminate, patterning thephotosensitive layer to expose the electrically conductive layer,copper-plating the exposed electrically conductive layer to form acopper layer, and removing remaining photosensitive resin and theelectrically conductive layer below the remaining photosensitive resin.

BEST MODE FOR CARRYING OUT THE INVENTION

The heat-resistant polymer film used in the present invention has amelting temperature (melting point) of at least 250° C., preferably atleast 300° C. Examples of the polymer film include polyimide films,aromatic polyamide films, liquid crystal polyester films, polyethersulfone films, polyether-ether ketone films, polyparabanic acid films,polyvinyl fluoride films and polyether imide films.

For reasons of heat resistance, polyimide films, aromatic polyamidefilms and liquid crystal polyester films are preferred. More preferredare polyimide films.

A polyimide resin is a conventionally well known resin and is generallyobtainable by polycondensation of an aromatic tetracarboxylicdianhydride with an aromatic diamine used as main components.

Examples of the aromatic tetracarboxylic dianhydride which constitutesthe polyimide resin include pyromellitic dianhydride,3,3′,4,4′-benzophenone tetracarboxylic dianhydride,2,2′,3,3′-benzophenone tetracarboxylic dianhydride,2,3,3′,4′-benzophenone tetracarboxylic dianhydride,naphthalene-2,3,6,7-tetracarboxylic dianhydride, naphthalene 1 2 56-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylicdianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride,naphthalene-1,2,6,7-tetracarboxylic dianhydride,4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylicdianhydride,4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-2,3,6,7-tetracarboxylicdianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylicdianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylicdianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylicdianhydride and 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylicdianhydride, although not limited to these examples.

Additionally, 3,3′,4,4′-diphenyltetracarboxylic dianhydride,2,2′,3,3′-diphenyltetracarboxylic dianhydride,2,3,3′,4′-diphenyltetracarboxylic dianhydride,3,3″,4,4″-paraterphenyltetracarboxylic dianhydride,2,2″,3,3″-paraterphenyltetracarboxylic dianhydride,2,3,3″,4″-paraterphenyltetracarboxylic dianhydride,2,2-bis(2,3-dicarboxyphenyl)propane dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,bis(2,3-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)etherdianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride,bis(3,4-dicarboxyphenyl)methane dianhydride,bis(2,3-dicarboxyphenyl)sulfone dianhydride,bis(3,4-dicarboxyphenyl)sulfone dianhydride,1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride,1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride,perylene-2,3,8,9-tetracarboxylic dianhydride,perylene-3,4,9,10-tetracarboxylic dianhydride andperylene-4,5,10,11-tetracarboxylic dianhydride may be mentioned.

Moreover, there may be mentioned perylene-5,6,11,12-tetracarboxylicdianhydride, phenanthrene-1,2,7,8-tetracarboxylic dianhydride,phenanthrene-1,2,6,7-tetracarboxylic dianhydride,phenanthrene-1,2,9,10-tetracarboxylic dianhydride,cyclopentane-1,2,3,4-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride,pyrrolidine-2,3,4,5-tetracarboxylic dianhydride,thiophene-2,3,4,5-tetracarboxylic dianhydride and, 4,4′-oxydiphthalicdianhydride. The aromatic tetracarboxylic dianhydride is not limited tothese examples. These compounds may be used singly or as a mixture oftwo or more thereof.

Examples of the diamine component include3,3′-dimethyl-4,4′-diaminobiphenyl, 4,6-dimethyl-m-phenylenediamine,2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4′4-methylenedi-o-toluidine, 4,4′-methylene 2,6-xylidine, 4,4′-methylene2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine,p-phenylenediamine, 4,4′-diaminodiphenylpropane,3,3′-diamino-diphenylpropane, 4,4′-diaminodiphenylethane,3,3,-diaminodiphenylethane, 4,4′-diaminodiphenylmethane,3,3′-diaminodiphenylmethane and2,2-bis[4-(4-aminophenoxy)phenyl]propane, although not limited to theseexamples.

Additionally, 4,4′-diaminodiphenylsulfide, 3,3′-diaminodiphenylsulfide,4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfone,4,4′-diaminodiphenyl ether, 3,3-diaminodiphenyl ether, benzidine,3,3′-diaminobiphenyl, 3,3′-dimethyl-4,4′-diaminobiphenyl,3,3′-dimethoxybenzidine, 4,4′-diamino-p-terphenyl,3,3′-diamino-p-terphenyl, bis(p-aminocyclohexyl)methane,bis(p-β-amino-t-buthylphenyl)ether,bis(p-β-methyl-δ-aminopentyl)benzene,p-bis(2-methyl-4-aminopentyl)benzene,p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene,2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene,2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine,m-xylylenediamine, p-xylylenediamine, may be mentioned.

Moreover, there may be mentioned 2,6-diaminopyridine,2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine,1,3-bis(3-aminophenoxy)benzene, 2,5-diaminophenol, 3,5-diaminophenol,4,4′-(3,3′-dihydroxy)diaminobiphenyl,4,4′-(2,2′-dihydroxy)diaminobiphenyl,2,2′-bis(3-amino-4-dihydroxyphenyl)hexafluoropropane, 2,5-diaminobenzoicacid, 3,5-diaminobenzoic acid, 4,4′-(3,3′-dicarboxy)diaminobiphenyl,3,3′-dicarboxy-4,4′-diaminodiphenyl ether, ω,ω′-bis(2-aminoethyl)polydimethylsiloxane, ω,ω′-bis(3-aminopropyl)polydimethylsiloxane,ω,ω′-bis(4-aminophenyl) polydimethylsiloxane,ω,ω′-bis(3-aminopropyl)polydiphenylsiloxane andω,ω′-bis(3-aminopropyl)polymethylphenylsiloxane. The diamine componentis not limited to these examples. These compounds may be used singly oras a mixture of two or more thereof.

The reaction of the acid anhydride compound with the diamine compound ina polar solvent gives a polyamic acid solution which is a precursor of apolyimide.

A polyimide film may be generally obtained by casting the polyamic acidsolution on a substrate. The cast solution is dried and then subjectedto imidization at a high temperature. Alternately, the solution isheated to effect the imidization. The resulting solution is cast on asubstrate, dried and heat-treated to give the film.

The heat-resistant polymer film used in the present invention may beconstructed into a multi-layered structure or may be compounded withvarious kinds of additives, if desired.

Further, a surface of the polymer film may be previously mechanicallyroughened or chemically activated for enhancing the adhesion strength.

Furthermore, for the purpose of improving the adhesion between thepolymer film and the plasma CVD layer of an organic metal compound, alayer of various resins which has a thickness of 0.1 to 5 μm, preferably0.5 to 3 μm, and which has high adhesiveness may be provided on thatsurface of the polymer film which is to be overlaid with the plasma CVDlayer. Particularly preferable is to provide a fluorinated polyimideresin layer or a silicone-polyimide resin layer having a thickness of 5μm or less.

The fluorinated polyimide resin may be obtained by using, as at leastpart of the above-described acid anhydride compound for the productionof polyimide resin, a fluorine group-containing acid anhydride such as2,2-bis(3-phthalic anhydride)hexafluoropropane or2,2-bis{phenylether(3-phthalic anhydride)}hexafluoropropane and/or byusing, as at least part of the above-described amine compound, afluorine group-containing diamine compound such as2,2-bis{4-(4-aminophenoxy)phenyl}-hexafluoropropane,2,2-bis(4-aminophenyl)hexafluoropropane,2,2-bis(3-amino-4-methylphenyl)hexafluoropropane,2,2′-(trifluoromethyl)benzidine or2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.

It is preferred that the silicone-polyimide resin contain at least 10mole % of the above-mentioned silicone-diamine compound based on a totaldiamine compounds for reasons of adhesion strength. The suitable contentof the silicone-diamine compound is 20 to 80 mole %.

While the heat-resistant polymer film may have any thickness, thethickness thereof is preferably 10 to 150 μm for the standpoint of thefabrication of flexible printed wiring boards. A thickness below 10 μmwill result in low stiffness and in poor machinability. Too large athickness in excess of 150 μm will cause a difficulty in machining suchas bending.

The plasma CVD layer of an organic metal compound is formed on at leastone side of the thus fabricated heat-resistant polymer film by anysuitable known method such as glow discharge in the vapors of theorganic metal compound.

Preferably, a discharge voltage of at least 1,000 V is applied betweenelectrodes in an inside electrode-type low temperature plasma generatingapparatus to cause glow discharge. A surface of the heat-resistantpolymer film is treated in the low temperature plasma atmosphere.

The low temperature plasma treatment is carried out in the presence ofan inorganic gas such as helium, neon, argon, nitrogen, oxygen, air,nitrous oxide, nitrogen monoxide, nitrogen dioxide, carbon monoxide,carbon dioxide, ammonia, steam, hydrogen, sulfur dioxide or hydrogencyanide. These inorganic gases may be used singly or as a mixture of twoor more thereof.

The gas atmosphere within the apparatus preferably has a total pressureof 0.001-10 Torrs, more preferably 0.1 to 1.0 Torr. A total pressure oflower than 0.001 or higher 10 Torrs is not preferable because thedischarge is not stable.

Under such a gas pressure, an electric power of 10 W to 100 KW by highfrequency of 10 KHz to 2 GHz is applied between the discharge electrodesto cause stable glow discharge. The discharge frequency band is notlimited to the high frequency. Low frequency, microwave or directcurrent may be also usable.

The low temperature plasma generating apparatus is desirably of aninternal electrode-type. However, an external electrode-type apparatusis used, if necessary. Capacitive coupling such as a coil furnace orinductive coupling may be adopted.

The shape of the electrodes is not specifically limited. Thus, theelectrodes may be in various forms such as flat plate-like, ring-like,rod-like or cylinder-like forms. Further, an electrically groundedinside metal wall of the treatment apparatus may be used as one of theelectrodes.

In order to maintain stable low temperature plasma by applying a voltageof 1,000 V or more between the electrodes, it is necessary to use aninput electrode provided with an insulation coating having a highwithstand voltage. When a naked metal electrode such as copper, iron oraluminum is used, arc discharge is apt to be caused. Thus, the surfaceof the electrode is desirably provided with a coat such as an enamelcoat, a glass coat or a ceramic coat.

The organic metal compound used in the present invention is notspecifically limited as long as it permits plasma CVD and has a boilingpoint of 50 to 400° C., preferably 100 to 300° C.

As the organic metal compound, any compound containing a metal such asSi, Ti, Al, B, Mo, Ni or Zn may be arbitrarily selected. The preferredorganic metal compound is at least one member selected from organicsilicon compounds, organic titanium compounds and organic aluminumcompounds.

The organic silicon compound is a compound having a Si atom to which atleast one hydrocarbyl group or hydrocarbyloxy group is bonded. Such anorganic silicon compound may involve an organic monosilane compoundrepresented by the following general formula (1):

wherein A¹ through A⁴ each represent a hydrocarbyl group or ahydrocarbyloxy group with the proviso that at least one of A¹ throughA⁴, preferably one to three of A¹ through A⁴, is a hydrocarbyloxy group.

The hydrocarbyl group may be an aliphatic hydrocarbyl group having 1 to18 carbon atom or an aromatic hydrocarbyl group having 6 to 18 carbonatoms. The aliphatic hydrocarbyl group may be a liner aliphatichydrocarbyl group having 1 to 18 carbon atoms or a cyclic aliphatichydrocarbyl group having 4 to 18 carbon atoms. The linear aliphatichydrocarbyl group may be an alkyl group having 1 to 18, preferably 1 to10, more preferably 1 to 4 carbon atoms or an alkenyl group having 2 to18, preferably 2 to 10, more preferably 2 to 4 carbon atoms. The cyclicaliphatic hydrocarbyl group may be a cycloalkyl group or a cycloalkenylgroup each having 4 to 18, preferably 5 to 10, more preferably 6 to 8carbon atoms.

The aromatic hydrocarbyl group may be an aryl group having 6 to 18,preferably 6 to 14, more preferably 6 to 10 carbon atoms or an arylalkylgroup having 7 to 18, preferably 7 to 14, more preferably 7 to 10 carbonatoms.

Specific examples of the hydrocarbyl group include methyl, ethyl,propyl, hexyl, decyl, vinyl, 3-butenyl, cyclohexyl, cyclooctyl,cyclododecyl, cyclohexenyl, cyclooctynyl, phenyl, tolyl, xylyl,phenethyl, benzylphenyl, benzyl, phenethyl, phenylbenzyl, andnaphthylmethyl.

The hydrocarbyl group may have a substituent which is inert to thereaction and which is able to be bonded to a carbon atom. Examples ofthe substituent include a halogen atom, a hydroxyl group, a cyano group,an amino group, a substituted amino group (e.g. methylamino,dimethylamino), an alkoxy group (e.g. methoxy, ethoxy) and analkoxycarbonyl group (e.g. methoxycarbonyl).

The hydrocarbyl group of the hydrocarbyloxy group may be an aliphatichydrocarbyl group having 1 to 10 carbon atoms or an aromatic hydrocarbylgroup having 6 to 12 carbon atoms. The aliphatic hydrocarbyl group maybe an alkyl group having 1 to 10, preferably 1 to 6, more preferably 1to 4 carbon atoms or an alkenyl group having 2 to 10, preferably 2 to 6,more preferably 2 to 4 carbon atoms. The cyclic hydrocarbyl group may bea cycloalkyl group or a cycloalkenyl group each having a having 4 to 12,preferably 5 to 10, more preferably 6 to 8 carbon atoms. The aromatichydrocarbyl group may be an aryl group having 6 to 12, preferably 6 to10, more preferably 6 to 8 carbon atoms or an arylalkyl group having 7to 12, preferably 7 to 10, more preferably 7 to 8 carbon atoms. Thesehydrocarbyl groups may have a substituent.

Examples of the hydrocarbyloxy group include alkoxy groups (e.g.methoxy, ethoxy and butoxy), aryloxy groups (e.g. phenoxy and naphthoxy)and arylalkyloxy groups (e.g. benzyloxy, phenethyloxy andnaphthylmethoxy).

In the above-described organic monosilane compound, the average carbonnumber per one Si atom contained therein is 4 to 30, preferably 4 to 10.Specific examples of the organic monosilane compound includetetraethoxysilane, tetramethoxysilane, methyltrimetoxysilane,methyltriethoxysilane, methyldiethoxysilane, diethyldiethoxysilane,dimethyldiethoxysilane, dimethyldimethoxysilane, dimethylethoxysilane,ethyltriethoxysilane, ethyltrimethoxysilane, triethylethoxysilane,trimethylethoxysilane, dimethyldipropoxysilane, n-butyltrimethoxysilane,acetoxypropyltrimethoxysilane, acetoxytrimethylsilane,2-(acryloxyethoxy)trimethylsilane,(3-acryloxyprophyl)dimethylmethoxysilane,(3-acryloxyprophyl)methyldimethoxysilane,(3-acryloxyprophyl)trimethoxysilane,3-(N-allylamino)-propyltrimethoxysilane, allylaminotrimethylsilane,allyldimethoxysilane, allyltriethoxysilane, allyltrimethoxysilane,4-aminobutyltriethoxysilane,N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,3-aminopropylmethyldiethoxysilane, 3-aminopropyltriethoxysilane,(3-glycidoxypropyl)-dimethylethoxysilane,(3-glycidoxypropyl)-methyldiethoxysilane,(3-glycidoxypropyl)-methyldimethoxysilane,(3-glycidoxypropyl)trimethoxysilane, 3-mercaptopropyltriethoxysilane,3-mercaptopropyl-trimethoxysilane, methacryloxypropyltrimethoxysilane,methacryloxypropyltris(methoxyethoxy)silane,N-phenylaminopropyltrimethoxysilane, phenyltriethoxysilane,vinylmethyldiethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane.

In addition to the above-described organic monosilane compound, theorganic silicone compound used in the present invention may be anorganic polysilane compound or an organic polysiloxane compound.

The organic polysilane compound is one which contains generally 2 to 20Si atoms in one molecule thereof and in which each of the Si atoms hasat least one hydrocarbyl or hydrocarbyloxy group bonded thereto. As thehydrocarbyl group of the polysilane compound, there may be mentionedvarious hydrocarbyl groups indicated above with reference to the organicmonosilane compound.

In the above-described organic polysilane compound, the average carbonnumber per one Si atom contained therein is 2 to 30, preferably 2 to 10.

Specific examples of the organic polysilane compound includehexamethyldisilane, hexaethyldisilane, 1,2-diphenyltetramethyldisilaneand hexamethoxydisilane, hexaphenyldisilane.

The organic siloxane compound is a compound which has a SiOSi linkage inthe molecular chain thereof. In the case of the present invention, thenumber of the SiOSi linkage is 1 to 20, preferably 1 to 10. Each Si atomhas 1 to 2 hydrocarbyls or hydrocarbyloxys bonded thereto. As thehydrocarbyl and hydrocarbyloxy groups of the siloxane compound, theremay be mentioned various hydrocarbyl and hydroxarbyloxy groups indicatedabove with reference to the organic monosilane compound. The organicpolysiloxane compound may be one which has a recurring unit representedby the following general formula (2):

wherein A¹ and A² each represent a hydrocarbyl group or a hydrocarbyloxygroup which may have a substituent. As the hydrocarbyl andhydrocarbyloxy groups of the polysiloxane compound, there may bementioned various hydrocarbyl and hydroxarbyloxy groups indicated abovewith reference to the organic monosilane compound.

Specific examples of the organic siloxane compound includehexamethylsiloxane, vinyltetramethylsiloxane, polydimethylsiloxanehaving a number average molecular weight 1 to 1000.

The organic titanium compound used in the present invention is acompound having a Ti atom to which at least one hydrocarbyl group, ahydrocarbyloxy group or a hydrocarbyl group-substituted amino group isbonded. Such an organic titanium compound may be a compound representedby the following general formula (3):

wherein at least one of A¹ through A⁴ represents a hydrocarbyl group, ahydrocarbyloxy group or a hydrocarbyl group-substituted amino group. Asthe hydrocarbyl and hydrocarbyloxy groups of the organic titaniumcompound, there may be mentioned various hydrocarbyl and hydroxarbyloxygroups indicated above with reference to the organic monosilanecompound.

Specific examples of the organic titanium compound include titaniumtetraethoxide, titanium tetramethoxide, titanium tetraisopropoxide,tetrakis (dimethylamino)titanium and tetrakis(diethylamino) titanium.

The organic aluminum compound used in the present invention is acompound having a Al atom to which at least one hydrocarbyl group or ahydrocarbyloxy group is bonded. Such an organic aluminum compound may bea compound represented by the following general formula (4):

wherein at least one of A¹ through A³ represents a hydrocarbyl group ora hydrocarbyloxy group. As the hydrocarbyl and hydrocarbyloxy groups ofthe organic aluminum compound, there may be mentioned varioushydrocarbyl and hydroxarbyloxy groups indicated above with reference tothe organic monosilane compound.

Specific examples of the organic aluminum compound include aluminumtri(isopropoxide), tri(ethoxy)aluminum, aluminum butoxide and aluminiumphenoxide.

Further, the organic aluminum compound used in the present invention maybe an organic complex compound of aluminum such as aluminiumacetylacetonato, aluminum ethylacetoacetate, aluminum methacrylate,aluminum pentanedionate.

By subjecting one or both sides of the heat-resistant polymer film toplasma CVD using the above-described organic metal compound, a plasmaCVD layer may be formed on one or both sides of the heat-resistantpolymer film. The CVD layer has a chemical structure containing part oforganic residues in addition to the metal. Such a CVD layer thusproduced may be subjected to a heat treatment or to a plasma treatmentagain in an inorganic gas atmosphere so as to remove unnecessary organicresidues. The plasma CVD layer has a thickness of 0.01 to 1 μm,preferably 0.02 to 0.1 μm.

The plasma CVD layer serves to improve the adhesiveness and to functionas a barrier to oxygen and moisture.

An electrically conductive layer is provided on the thus obtained plasmaCVD layer. As the conductor, any conductive metal may be used. From thestandpoint of etching property, copper is suitably used. As long as theetching property is not adversely affected, a different metal such as Nior Cr may be provided in the interface for various desired purposes.

An electroless plating method, a vacuum deposition method, a sputteringmethod, etc. may be adopted for the formation of the electricallyconductive layer. For reasons of adhesion strength, a sputtering methodis suitably used.

The thickness of the electrically condutive layer may be arbitrarilydetermined depending upon the need for the desired circuit. From thestandpoint of economy, a thickness of 1 μm or less is preferred in thecase of a sputtered layer.

When a design of the circuit requires a large copper thickness, theconductive layer can be thickened by electrolytic plating using thesputtered layer as an electrode. In such a case, the thickness of theconductive layer is preferably 20 μm or less from the standpoint ofstress during the plating. In general, the thickness of the electricallyconductive layer is 1 to 20 μm, preferably 3 to 12 μm.

A surface layer containing any organic or inorganic rust preventionagent may be provided on a surface of the electrically conductive layerfor the prevention thereof from oxidation.

A flexible circuit board may be obtained by subjecting the electricallyconducitive layer, formed by overlaying a plating layer on the sputteredlayer, in any customarily employed method including masking, patterningand etching.

For the formation of more precise flexible circuit board, asemi-additive method may be employed. In this method, a photosensitiveresin layer is provided over the sputtered layer. The resin layer isthen patterned to expose the sputtered layer. Using the exposedsputtered layer as an electrode, an electrolytic plating is carried outto form a thick copper layer thereon. Thereafter, the remainingphotosensitive resin layer and the sputtered layer beneath thephotosensitive layer are removed to obtain a flexible circuit board.

EXAMPLE

The present invention will be next concretely described by exampleswhich are not, however, restrictive of the present invention.

In the examples and comparative examples, the adhesion strength wasmeasured as follows. Copper plating was performed to obtain a copperlayer having a thickness of 10 μm. This was subjected to etching toobtain a linear wiring having a width of 2 mm. The film-side surface ofthe board was lined with an aluminum plate with a thickness of 1 mmusing a double coated adhesive tape. The wiring was drawn at a rate of 5cm/minute in a direction of 180 degrees to measure the peel strength.

The coefficient of thermal expansion, water absorption coefficient, andsolder-proof property are measured as follows.

A thermomechanical analyzer (manufactured by Seiko Instruments Co.,Ltd.) was used for the measurement of the coefficient of thermalexpansion. A sample was heated to 255° C. and maintained at thattemperature for 10 minutes. Then, the heated sample was cooled at a rateof 5° C./minute. An average coefficient of thermal expansion(coefficient of thermal expansion) from 240° C. to 100° C. wasdetermined.

A sample film was immersed in water at 25° C. for 24 hours for themeasurement of the water absorption efficiency. The film was then takenout from the water and the weight thereof was measured after thesurfaces thereof had been lightly wiped. The water absorptioncoefficient was determined from the change in weight of the film beforeand after the immersion.

To measure the solder-proof property, a sample laminate was allowed toabsorb water until the above-described saturated point. The sample wasthen immersed in solder baths having temperatures varying at an intervalof 10° C. The solder-proof property is the highest temperature of thesolder below which no bulge occurred.

The abbreviations used in the examples are as follows:

DAPE: 4,4′-diaminodiphenyl ether

BAPB: 4,4′-bis(3-aminophenoxy)biphenyl

BAPP: 2,2′-bis[4-(4-aminophenoxy)phenyl]propane

PMDA: pyromellitic dianhydride

BPDA: 3,3′,4,4′-biphenyltetracarboxylic dianhydride

6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride

DMAc: N,N-dimethylacetamide

Synthesis Example 1

425 Grams of DMAC was provided in a one-liter separable flask, intowhich 0.05 mol of DAPE and 0.05 mol of BAPP were dissolved withstirring. Next, 0.1 mol of 6FDA was added thereto under the nitrogen airflow. Then, the polymerization reaction was performed with continuousstirring to obtain a viscous solution of polyimide precursor A.

Synthesis Example 2

425 Grams of DMAc was provided in a one-liter separable flask, intowhich 0.1 mol of BAPB was dissolved with stirring. Next, 0.1 mol of BPDAwas added thereto under the nitrogen air flow. Then, the polymerizationreaction was performed with continuous stirring to obtain a viscoussolution of polyimide precursor B.

Example 1

KAPTON EN Film (38 μm in thickness) manufactured by Toray Industries,Inc. was secured to a drive drum of a vacuum device. Then the device wasmade vacuum to 0.001 Torr. Next, tetramethoxysilane vapors wereintroduced into the vacuum system, and the pressure was controlled at0.20 Torr. A high-frequency voltage of 13.5 MHz was applied to a surfaceof the film so that one side of the film was subjected to a plasmatreatment at a discharge power density of 300 W·min/m². Thereby, aplasma CVD layer composed mainly of SiO was formed.

Further, using a sputtering device, the plasma-treated surface of thefilm was subjected to sputtering to deposit copper to a thickness of3000 angstroms. Using the copper layer as an electrode, an electrolyteplating was carried out to form a copper layer with a thickness of 10μm.

The measurement of the copper layer revealed that the adhesion strengththereof was 0.6 kg/cm. The laminate film was heat treated at 150° C. ina recirculating-type oven for 10 days. Then, the laminate was measuredfor the adhesion strength in the same manner as above. The adhesivestrength was found to be unchanged and 0.6 kg/cm. The water absorptionefficiency of the KAPTON EN Film was found to be 2.0%. The coefficientof thermal expansion was found to be 2×10⁻⁵/° C. The solder-proofproperty of the film laminate was found to be 280° C.

Example 2

In Example 1, prior to the plasma treatment, a vanish of the polyimideprecursor A was applied to the film such that the thickness of thecoating after drying and curing was 1 μm. The vanish thus applied wasthen heated to 270° C. to perform a heat treatment.

The resulting film was then subjected to a plasma treatment and coppersputtering treatment in the same manner as that in Example 1. The copperlayer was measured for the adhesion strength. The initial adhesionstrength was found to be 1.0 kg/cm and to be unchanged after a heattreatment at 150° C. The solder-proof property was found to be 280° C.

Example 3

In Example 1, prior to the plasma treatment, a vanish of the polyimideprecursor B was applied to the film such that the thickness of thecoating after drying and curing was 1 μm. The vanish thus applied wasthen heated to 270° C. to perform a heat treatment.

The resulting film was then subjected to a plasma treatment and coppersputtering treatment in the same manner as that in Example 1. Themeasurement of the adhesion strength revealed that the initial adhesionstrength was 0.8 kg/cm and was unchanged after a heat treatment at 150°C. The solder-proof property was found to be 280° C.

Example 4

In Example 2, the tetramethoxysilane was substituted bypolydimethylsiloxane SH-200 (manufactured by Toray Dow Silicone Inc.)having a number average molecular weight of 1˜2. The test was performedin the same manner.

The thus obtained laminate had an initial adhesion strength of 0.9kg/cm. After 10 days at 150° C., the adhesion strength was 0.9 kg/cm.The solder-proof property was 290° C.

Example 5

In Example 2, the tetramethoxysilane was substituted by titaniumtetramethoxide. The test was performed in the same manner.

The thus obtained laminate had an initial adhesion strength of 0.9kg/cm. After 10 days at 150° C., the adhesion strength was 0.8 kg/cm.The solder-proof property was 290° C.

Example 6

The test was performed such that, in Example 1, the KAPTON EN wassubstituted by APICAL HP Film (manufactured by Kanegafuchi Kagaku)having a thickness of 38 μm.

The thus obtained laminate had an initial adhesion strength of 0.9kg/cm. After 10 days at 150° C., the adhesion strength was 0.9 kg/cm.The solder-proof property was 320° C. The water absorption coefficientof APICAL HP Film was 1.5%. The coefficient of thermal expansion wasfound to be 1×10⁻⁵/° C.

Example 7

The test was performed such that, in Example 2, the KAPTON EN wassubstituted by a liquid crystal polyester film (manufactured by JapanGore Inc.) having a thickness of 50 μm.

The thus obtained laminate had an initial adhesion strength of 0.7kg/cm. After 10 days at 150° C., the adhesion strength was 0.7 kg/cm.The solder-proof property was 400° C. The water absorption coefficientof the liquid crystal polyester film was 0.3%. The coefficient ofthermal expansion was found to be 5×10⁻⁶/° C.

Example 8

In Example 2, a photosensitive dry film (thickness: 25 μm) was laminatedon the laminate which had been subjected to the sputtering. Thephotosensitive dry film was then exposed and developed for patterning.The exposed sputtered layer was subjected to electrolytic copper platingin the same manner as that in Example 2. After the resist layer had beenremoved, the sputtered Cu layer was slightly etched using a ferricchloride solution.

The thus obtained wiring had the same properties as those of Example 2.

Comparative Example 1

A laminate was prepared in the same manner as that in Example 1 exceptthat no plasma treatment was carried out.

The thus obtained laminate had an initial adhesion strength of 0.3kg/cm. After 10 days at 150° C., the adhesion strength was 0.1 kg/cm.The solder-proof property was 230° C.

Comparative Example 2

A laminate was prepared in the same manner as that in Example 2 exceptthat no plasma treatment was carried out.

The thus obtained laminate had an initial adhesion strength of 0.6kg/cm. After 10 days at 150° C., the adhesion strength was 0.1 kg/cm.The solder-proof property was 240° C.

1. A film laminate comprising a heat-resistant polymer film, a plasmaCVD layer of an organic metal compound provided on at least one side ofsaid heat-resistant polymer film, and an electrically conductive layerprovided on said plasma CVD layer.
 2. The film laminate as recited inclaim 1, wherein said organic metal compound includes at least onemember selected from the group consisting of organic silicon compounds,organic titanium compounds and organic aluminum compounds.
 3. The filmlaminate as recited in claim 1, wherein said heat-resistant polymer filmis at least one member selected from the group consisting of aromaticpolyimide films, liquid crystal polyester films and aromatic polyamidefilms.
 4. The film laminate as recited in claim 1, wherein saidheat-resistant polymer film is an aromatic polyimide film having a waterabsorption coefficient of 2% or less and a linear expansion coefficientof 2×10⁻⁵/° C. or less.
 5. The film laminate as recited in claim 1,additionally comprising a resin layer which has a thickness of 5 μm orless, which is provided between said heat-resistant polymer layer andsaid plasma CVD layer and which contains a fluorinated polyimide resinor a silicone-polyimide resin.
 6. The film laminate as recited in claim1, wherein said electrically conductive layer is a copper layer formedby a sputtering method and having a thickness of 1 μm or less.
 7. Thefilm laminate as recited in claim 1, wherein said electricallyconductive layer is a two-layered copper layer having a total thicknessof 20 μm or less and composed of a copper layer formed by a sputteringmethod and an electrolytic copper layer formed by an electrolyticplating using said copper layer as an electrode.
 8. A flexible circuitboard comprising a film laminate according to claim 1 with saidelectrically conductive layer being patterned to form a circuit, and acopper plating layer provided on said circuit.
 9. A flexible circuitboard obtainable by a method comprising forming a photosensitive resinover said electrically conductive layer of a film laminate according toclaim 1, patterning said photosensitive layer to expose saidelectrically conductive layer, copper-plating said exposed electricallyconductive layer to form a copper layer, and removing remainingphotosensitive resin and said electrically conductive layer below saidremaining photosensitive resin.